In the art of torque wrenches and similar tools provided to apply predetermined torsional forces onto and through threaded fasteners and the like in various structures and machines, there is a special class of torque multiplying and force indicating wrench which is provided to apply torque to fasteners of particular machines, which is such that parts of the machines, adjacent the fastenrs, establish the reaction parts or structures necessary to generate the required torsional forces. That is, the applied torsional forces are generated between the fasteners and adjacent related reactive structure, not between the fasteners and some remote unrelated reaction structures.
The above noted special class of torque wrench typically includes a case housing a suitable torque multiplying drive means with torque input and output members or parts, work or fastener engaging parts, such as drive sockets, drivingly engaged with and between the torque output part and a related fastener and a reaction member or part in driving engagement with and between the case of the wrench and the structure with which the fastener is related. Further, the torque which is applied by such wrenches is typically measured by force indicating means engaged with and between the reaction parts and the wrench cases.
The most common prior art wrench of the special class here concerned with is that wrench which is disclosed in U.S. Pat. No. 3,683,686 for "MECHANICAL TORQUE WRENCH AND HYDRAULIC READOUT THEREFOR", issued Aug. 15, 1972.
In the above noted prior art wrench structure, the reaction part is an annular part with a central opening which freely rotatably accommodates an output spindle of the wrench which is adapted to be drivingly coupled to a related fastener by means of a drive socket or the like. The reaction part has a pair of lock pins which engage in lock pin receiving sockets or openings in the machine or structure with which the fastener to be worked upon is related and has a pair of opposite, radially outwardly projecting lever arms. The lever arms extend freely between related pairs of spaced stop posts formed on the wrench case. The lever arms carry fluid filled bellows and the stop posts have adjustable stops to engage the bellows whereby relative rotation of the reaction part and the wrench case results in the exerting of forces on the bellows. The bellows are connected with a suitable hydraulic pressure gauge which indicates the forces applied to the bellows and which is calibrated to indicate the forces applied by the wrench structure onto a fastener worked upon thereby.
While the above noted prior art wrench has proven to be serviceable, the hydraulic force sensing and indicating means thereof is not nearly so accurate as are most other kinds and classes of high quality torque indicating wrenches and tools. The hydraulic force sensing and readout means noted above is fragile and subject to being damaged or otherwise adversely affected in normal use and handling of the noted wrench structure.
The general acceptance and use of the noted prior art wrench structure in industry is believed and understood to be due to the fact that no other like or similar wrench structure with other or different force indicating and readout means has been developed by the prior art and made available.